The Growth of the Mandible

Growth of The Mandible & Maxilla

The Mandible

Is the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved,

horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly

at right angles.

The growth and development of an individual is divided into two periods

1. Prenatal period 2. Postnatal period

The prenatal life is divided into 3 periods :

1 .Period of the ovum2 .Period of the embryo

3 .Period of the fetus

Prenatal growth phase

About the 4th week of intrauterine life, the pharyngeal arches are laid down .

∞The first arch is called the mandibular arch .

∞The second arch is called the hyoid arch .

Each of these five arches contain :

A central cartilage rod that form the skeleton of the arch

A muscular component termed as bronchomere

A vascular component A neural component

INTRAMEMBRANOUS BONE FORMATION The first structure to develop in the

primodium of the lower jaw is the mandibular division of trigeminal nerve that precedes the mesenchymal condensation forming the first [mandibular] arch.

•At around 36 -38 days of intrauterine life there is ectomesenchymal condensation

•Some mesenchymal cells enlarges , acquire a basophilic cytoplasm and form osteoblasts

•These osteoblasts secrete a gelatinous matrix called osteoid and result in ossification of an osteogenic membrane.

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•The resulting intramembranous bone lieslateral to meckel’s cartilage of first [mandibular ] arch

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•In the sixth week of the intrauterine life a single ossification centre for each half of the mandible arises in the bifurcation of inferior alveolar nerve into mental and incisive.

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•During seventh week of intrauterine life bone begin to develop lateral to meckel’s cartilage & continues until the posterior aspect is covered with bone 

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•Between eight & twelfth week of intrauterine life mandibular growth accelerate , as a result mandibular length increases.

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•Ossification stops at a point , which later become mandibular lingula , the remaining part of meckels cartilage continues to form sphenomandibular ligament from lingula to the spinous process of sphenoid.

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•Secondary accessory cartilage appear between tenth &fourteenth week of intrauterine life to form head of condyle , part of coronoid process & mental protuberance.

Growth of the Mandible The main sites of postnatal

mandibular growth are at: 1. Condylar cartilage 2. The coronoid process 3. The posterior border of the rami 4. The alveolar ridge

These areas are of bone opposition are account grossly for the increase in height, length and width of the mandible.

So, they are accompanied by selective resorption which results in:

a) modeling of the growing bone b) remodeling of the growing bone

The mandible grows in 3 planes :

Vertical Growth › Growth by secondary cartilage.

“ The secondary cartilage here is the condyle”

Antero-posterior growth

Transverse Growth › Subperiosteal bone apposition and bone resorption.

1.Vertical Growth

It’s the result of:

A) Growth at the condyle

B) Vertical growth of the body

A.Growth at the condyle

The condylar cartilage serves as an important centre of growth for the ramus and the body of the mandible.

A. Growth by secondary cartilage

( mainly condylar cartilage )

Increase in height of the

mandibular ramus

Increase in the over all length

of the mandible

Increase of the inter condylar distance

B.Vertical growth of the body of the mandible

This occurs by surface apposition of bone (periosteal apposition) along the upper border and results in an increase in height of the mandibular body.

Growth 2. Astero-posterior Occurs by:

A) Bone apposition on the posterior border of the ramus.

B) Sutural growth at the symphysis.

A.Bone apposition on the posterior border of the ramus This is accompanied by resorption

on the anterior border to maintain the proportion of the ramus and to give room for the erruption of the subsequent molars particularly the permanent ones.

The apposition resorption balance extends up to the coronoid process and the mandibular notch

┼ So we get:

1) bone resorption at the anterior border of the neck of the mandible.

2) Bone apposition at the posterior border of the coronoid process.

B.Sutural growth at the sympysis

This contributes with the antero-posterior growth of the mandible up to the end of the first year.

“Check the figure at the previous slide”

3.Transverse growth

The growth here occurs by periosteal apposition on the external surface of the mandible which results in increase in thickness.

Bone deposition

Bone resorption

Result in

External surface of

the mandible

Inner surface of

the mandible

Increase the transverse dimension

Posterior border of the remus

Anterior border of

the ramus

Adjust the thickness of the ramus

Anterior border of

the coronoid process

Posterior border of

the coronoid process

Displacement of the coronoid process

Chin region ــــــــــــــــــــــــ

Modeling of the lower

face

Age Changes of the mandible

1 .At birth

The body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal is of large size, and runs near the lower border of the bone; the mental foramen opens beneath the socket of the first deciduous molar tooth. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid process is of comparatively large size, and projects above the level of the condyle.

2 .At Childhood

The two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but more especially behind the mental foramen, to provide space for the three additional teeth developed in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles; but the alveolar portion is the deeper of the two, and, consequently, the chief part of the body lies above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the mylohyoid line; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°.

3 .Adulthood

The alveolar and subdental portions of the body are usually of equal depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°.

4 .Old age

The bone becomes greatly reduced in size, for with the loss of the teeth the alveolar process is absorbed, and, consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is close to the alveolar border. The ramus is oblique in direction, the angle measures about 140°, and the neck of the condyle is more or less bent backward.

the maxilla

The Maxilla The maxillæ are the largest bones of the face, excepting the mandible,

and form, by their union, the whole of the upper jaw. Each assists in forming the boundaries of three cavities, the roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and palatine.

Growth of the maxilla

1 .Sutural growth

2.Alveola-r process development

3 .Subperios-teal bone formation

4 .Enlargeme

nt of maxillary

sinus

5 .Bone resorbtio-

n and bone

depositio-n

1.Sultural Growth

It continues till 10 years of age then becomes less significant. The maxilla articulates with the other bones of the skull by 4 main sutures:

a) Frontomaxillary suture.

b) Zygomaticomaxillary suture.

c) Zygomaticotemporal suture.

d) Pterygopalatine suture.

All these sutures are parallel to each other

and directed from upward anteriorly to

downward posteriorly. So growth at these

sutures will shift the maxilla forward and

downward.

2 .Alveolar process development

It will add to the height of the maxilla. Eruption of teeth specially the

permenant set that serves much in this direction, while eruption of the

upper permenant molars adds to the lengt of the arch.

3 .Subperiosteal bone formation

Occures throughout life serves as a main factor for the growth of the

maxilla

4 .Enlargement of the maxillary sinus

It plays an important role in the growth of the body of the maxilla. The sinus, which occupies most of the body of the maxilla, expands by bone resorption on the sinus side and bone deposition on the facial surface of the maxillary process. A process known as pneumotization

5 .Bone resorption & bone deposition

Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal cavity compensated by bone deposition on the oral surface of the palate will aid in the enlargement of the nasal cavity and consequently increase the height of the maxilla

Occurs also in other sites than the sinus. Bone resorbtion at the floor of the nasal

cavity compensated by bone deposition on the oral surface of the palate will aid in the

enlargement of the nasal cavity and consequently increase the height of the

maxilla

AGE CHANGES OF THE MAXILLA

1 .AT birth

1. The transverse and antero-posterior diameters of the bone are each greater than the vertical.

2. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process.

3. the teeth sockets reaching almost to the floor of the orbit.

4. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose

2 .At Adulthood

In the adult the vertical diameter is the greatest due to:

a) The development of the

alveolar processb) Increase in size of the

sinus.

3 .At the old

In old age the bone reverts in some measure to the infantile condition as:

1. its height is diminished.

2. after the loss of the teeth the alveolar process is resorbed, and the lower part of the bone contracted and reduced in thickness.

References :FpBook:

http://www.fpnotebook.com/Dental/Anatomy/MndblAntmy.htm

Google books: http://preview.tinyurl.com/ccwhj38 Oxford Journals:http://ejo.oxfordjournals.org/content/24/1/69.full.pdfNcbI: http://www.ncbi.nlm.nih.gov/pubmed/18929270Angle : http://www.angle.org/doi/pdf/10.1043/0003-

3219(2002)072%3C0105:ALSOCG%3E2.0.CO%3B2Head Face Med: http://www.head-face-med.com/content/5/1/15

Presented by :

Suzanne Medhat Fahim: >Growth of the mandible

Abeer Fathy: >Age changes in the Mandible

Sarah Mamdouh Ashour: >The Maxilla

“Written & managed by: Suzanne Medhat Fahim”